Glassy samples with a composition of 40P2O5–30V2O5–(30-x)Li2O– xK2O, 0<x<30 (mol %) were prepared by the conventional melt quenching technique in two forms of bulk and blown film. X-ray diffraction patterns corroborated the amorphous feature of the samples. Density of samples was investigated by using Archimedes principle. Based on absorption and reflection spectra, indirect allowed optical gaps, Urbach energies, refractive index and dielectric coefficients were calculated. Study of FTIR spectra revealed that all of the samples mainly contain metaphosphate and pyrophosphate units. Glass transition temperatures were also evaluated using DSC curves. Non-linear variation of many physical properties by gradually substitution of Li ions with K, confirmed the existence of mixed alkali effect in glassy system.​